Soil Water Characteristics and structural stability of a Typic Paleustult Under Different Vegetation Cover.

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1 PAT June, 2012; 8 (1): ; ISSN: Online copy available at Publication of Nasarawa State University, Keffi Soil Water Characteristics and structural stability of a Typic Paleustult Under Different Vegetation Cover. Enyioko, C. O 1. Obi, M. E 2. and Eneje, R. C 3*. 1 Department of Forestry and Land Resources, Umuahia, Abia state. 2 Department of Soil Science, Faculty of Agriculture University of Nigeria Nsukka, Enugu State. 3 Department of Soil Science And Meteorology, Michael Okpara University of Agriculture Umudike, Nigeria. chizma2001@ yahoo.com Abstract The effect of different vegetation cover on soil water characteristics and aggregate stability of a Typic Paleustult was carried out. The different cover management practices were bare fallow, (BF), cassava cultivation (CS), groundnut cover (GN), manured groundnut cover GN+ PM) and Panicum maximum(pmc), while the soil properties studied were water drop energy(impact), macro porosity, micro porosity, saturated hydraulic conductivity, soil moisture content at 6kpa, soil aggregate stability, and penetration resistance. Data were subjected to analysis of variance using RCBD, and results show that soil resistance to penetration was highest in the bare fallow treatment (1.7kg/m 2 ) and lowest under the manured groundnut treatment (1.0kg/m 2 ), Soil total porosity and macro porosity were highest (50.84 and 24.4% respectively) under the manured groundnut treatment and lowest (43.16 and 16% respectively) under the cassava plot. Saturated hydraulic conductivity was lowest in the cassava plot (23.3cm/h) but highest in the manured groundnut plot. The management practices significantly increased the number of water drops and the energy required to breakdown soil aggregates to pass through a 4.75mm sieve. The highest drop number and energy values were obtained for aggregates formed under Panicum cover whereas the lowest values were obtained for aggregates of the bare soil The percent aggregate stability > 0.5 was not statistically significant but was highest for the Panicum maximum treatment closely followed by the bare fallow treatment and GN+PM treatment. The overall trend in changes in soil water properties (Ksat, PT, and macro-porosity) was BF CS<GN<PMC<GN+PM. Keywords: Soil water properties, Panicum maximum, bare fallow, penetration resistance, aggregate stability Introduction Soil water status affects soil properties either directly by its influence on soil weathering and profile development or indirectly on a short term basics by influencing soil factors such as soil strength, friability and permeability to water and solutes and gases. Unfortunately, most interest in soil water is centered on its content and availability with little or no regards for its interrelations with other soil properties and environmental factors. Soil characteristics such as infiltration, saturated hydraulic conductivity, soil porosity, and water retention and availability has been related to soil structure. Research works (Wood et. al, 1987) relating soil infiltration characteristics to land use for

2 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.154 instance found that ground cover control infiltration, while Lugo Lopez et. al, (1981) reported that infiltration is a function of soil properties such as bulk density, pore size distribution and aggregate stability. According to Adeoye (1982), deep tillage of Alfisol in Northern Nigeria result in increased porosity, while Tollner et. al, (1984) reported that beneficial effects of tillage on soil include an in increase the number of drainage pores in the soil. According to Papendick and Campell (1981), water retention in soils is influenced by texture, organic matter content and the physical composition of the soil. Soil with high amount of clay content and organic matter for instance hold considerably more gravimetric water at a given water potential than soil with a high content of sand. Also, Mbagwu and Ekwealor (1990) reported high moisture retention for different soils amended with brewer s spent grain, while Mbagwu (1989) reported that addition of organic matter at any rate significantly increased soil water retention except at 1.500kpa. However, for exposed soils especially highly degraded soils in the tropics water retention is reduced and this is attributable to runoff and possibly a reduction in porosity due to high bulk density. Therefore, in this study we set out to study the water characteristics of a Typic paleustult (Nkpologu sandy loam soil) under bare fallow, cassava cultivation, leguminous plant (groundnut) and grass plant (Panicum maximum) management. The main objective was to relate these characteristics of the soil as well as determine which of these cover crop management type best influenced the soil property for crop growth. Material and Methods Experimental site The experiment was carried out at the University of Nigeria Nsukka, teaching and Research farm located on latitude 06 o 5 2 N and longitude 07 o 24 E. The area has an annual rainfall of about 1700mm. The rainfall distribution is bimodal, a wet (April to October) and dry (November to March) season (Obi, 1982). The soil is deep, porous and red to brownish red derived from sandy deposits of false bedded sand stone. It is an Ultisol belonging to Nkpologu series and is classified as Typic paleustult (Nwadialo, 1989). Field layout The field was laid out in Randomized complete Block Design (RCBD) with four replications. Four treatments were applied on the plots of 4m X5m with 0.5m spacing between plots and 1m between replications. The treatments were as follows; ( i) Bare fallow (BF)- The land was placed under fallow and was kept free of weed and crop through out the period of research, weeding was done manually.

3 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.155 (ii) Cassava cultivation (CS); Cassava (Manihot esculentus var. NR8082) was planted on flats at a spacing of 1m X 1m giving a plant population of 10,000stands per hectare. (iii) Panicum maximum cultivation (PMC); Guinea grass was allowed to dominate this plot for about three years. (iv) Groundnuts (Arachis hypogea) cultivation (GN); Groundnuts was planted on the flat at a spacing of 25cm X 50 cm (intra and inter row respectively) giving a total plant population of 76,000stands per hectare which ensured proper ground cover. Sample collection Undisturbed soil samples were collected at the start of the experiment using core of dimensions 7.6X 7cm (length and diameter). Auger soil samples were also collected from0-15cm depth and both samples subjected to physical and chemical analysis. Laboratory Analysis Soil water content This was determined by the gravimetric method, the soil core samples were saturated in water and their weights at saturation were taken, then the samples are oven dried at c for 24hours. Dry samples were cooled in a desicator and reweighed again. Moisture content was computed as; Moisture content =Ww Dw x 100 Dw 1 Where; Ww = Wet weight of soil Dw = Dry weight of soil Soil bulk density, porosity and pore-size distribution Core samples were collected from experimental plots carefully trimmed and one end tied with calico cloth. The weight of core samples were taken and samples were soaked for 24hours in a pan containing about 5cm of water after 24hrs, the water level in the pan was raised to ensure complete saturation of the soil samples. Then the samples were weighed after 24hrs and placed on a tension table adjusted for 60cm of tension for 24hrs, the soil core samples were removed from the tension tables and weighed and oven-dried for 48hrs at a temperature of 105 o C and weighed again. Calculations were made as follows:

4 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.156 (i) Bulk density = Oven-dry mass(g) Vol of soil (cm3) (ii) Total porosity= Vol of water at saturation X 100 Vol of soil 1 (iii) Air space porosity= Vol of water drained at 60cm tension X 100 Vol. of soil 1 (iv) Capillary porosity= Vol of water retained at 60 cm tension X 100 Vol of soil 1 Saturated hydraulic conductivity This was determined using the modified Klute (1965), method Saturated hydraulic conductivity was calculated as follows: Ksat = QL HAT Where: Ksat = saturated hydraulic conductivity (cm/hr) ; Q= quantity of water (cm3) L= length of core (cm) ; H = hydraulic gradient (cm) A= cross-sectional area of core (cm2) ; T= Time elapsed (hr) Aggregate stability A modification of Yoders (1936) wet sieving technique was used to determine aggregate stability. The set of sieves used had size openings ranging from 2mm to 0.25mm (2, 1, 0.5 and 0.25mm). A 25g soil (pre-sieved through 4.25mm) was soaked for 5minutes on the top-most sieve. Shaking was done by vertically oscillating the set of sieve in water for 80 times. The resistant aggregates were carefully washed out of the sieve into evaporating dishes and oven-dried for about 24hrs. The sample weights were recorded. To correct for sand in the sample, soils in sieves of 2mm to 0.5mm were returned to a dish and soaked with 5ml of sodium hexametaphosphate. Enough water was added to cover the aggregates. Thereafter, the suspension was stirred for about 30 minutes and sand particles larger than 0.5mm were removed by washing dispersed aggregates through a 0.5mm sieve, the sand was washed into an evaporating dish and oven dried for 24hrs at a temperature of 105 o C, the weight of sand was taken. Aggregate stability was calculated using the formula: Percent aggregate stability (%AS) = wt of WSA>0.5mm-wt of sand X 100 Wt of sample-wt of sand 1

5 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.157 Other soil properties determined in the laboratory include, soil water retention, which was determined by the hanging column of water method as described by Richard (1957) using water retention at 60 cm tension. Soil particle size, was determined by the hydrometer method Bouyoucos (1951), with sodium hexameaphosphate as the dispersant. Total aluminum was determined by the method of Vogel (1961), and total iron determined by colorimetric methods AOAC (1970). Soil P H was determined in water and KCl in 1:2.5 soil water suspension using p H meter (Jackson 1958) Statistical Analysis Data obtained from the study were subjected to analysis of variance test in Randomized Complete Block Design as outlined by Steel and Torrie (1980). Simple linear correlation of selected parameters was carried out as described by Little and Hills (1972). Result and Discussions The soil used for this study is a sandy loam (Table 1). The dominance of sand fraction is attributable to the dominance of parent material, in this case, -false-bedded sandstone (Akamigbo and Igwe, 1990). The soil management practices increased organic matter content of the soil at the end of the experiment except the plot planted with groundnut alone that recorded a reduction in percent OC content in the soil at the end of the experiment (Table 3); this is expected since groundnut a legume could mobilize OC in the soil for profuse foliage production. Also the plant cover system resulted in reduced compaction in the soil as indicated by a reduction in bulk density of the soils except the plot planted up with cassava, which experienced an increase in bulk density indicating poor structural status of the soil since increased BD is associated with high clogging of soil pores and compaction with hard pan formation. The trend in BD explains the observation in the total porosity of where the percent age of pore space reduced up to 22% in the cassava plot. Also this result agree with the observation of Adekalu and Osunbitan (2001) that BD is indirectly affected by cultivation, thus variations in BD and macro porosity are attributable to land use. Earlier, Obi and Nnabude (1988), reported significant reduction in bulk density under continuous Centrosema pubesscens and Panicum maximum covers and attributed this to high root density and high organic matter accumulation under continuous covers. However the soil moisture content at 6kpa was highest in this same plot, indicating that compaction may have resulted in ponding of the soil. This agrees with the observation of Obi and Nnabude (1988), since an increase in bulk density is associated with

6 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.158 decreased pore volume and increased micro-porosity and pore space discontinuity, thus affecting the consistency of the soil and its capacity to conduct and retain water (Richards and Wadeigh, 1952). Table 1: Physico-chemical characteristics of soil at the start of the experiment Soil Property Mean value Sand (%) 61.3 Silt (%) 11.0 Clay (%) 27.7 Textural class Sandy loam Dry Bulk density(g/cm3) 1.48 Total porosity(%) Macro porosity(%) Micro porosity (%) Saturated hydrualic conductivity Infiltration rate (cm/h) Soil p H (H2O) 4.8 Soil p H (KCl) 3.8 Organic carbon (%) 0.84 Total Al(Meq/100soil) 0.24 Total Fe(Meq/100soil ) Aggregate Stability (%) Table 2: Property of the poultry manure used in the study Property Poultry manure OM (%) Total N (%) 2.86 Total P (%) 2.00 Total K (%) 1.50 C:N Ratio 7:1 C:P ratio 10:1

7 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.159 Table 3 : Soil Physicochemical properties at the end of the experiment. Soil property Land Management practice Bare Fallow Cassava Panicum Max. Groundnut Groundnut+Poultry Manure OM (%) Ns ph (H2O) Ns ph(kcl) Ns Fe (meq/100gsoil) Ns Al (meq/100gsoil) Fe/Al (meq/100gsoil) BD(mg/m 3 ) Ns Micro Ns Porosity(%) Macro Porosity(%) Total porosity (%) Ksat (cm/h) Soil moisture (6kpa) Water drop* Penetro-meter resistance( kg/m 2 ) Kinetic energy x x X X x10-6 AS >0.5 (%) Ns *Mean of 15 determinations F-LSD 0.05 Soil structural stability assessed by percent aggregate stability (AS>0.5) indicated stability was higher for all the cover crop management practice at the end of the experiment, however the plot supporting the Panicum maximium had the highest level of stability of micro aggregates (about 94%), this was closely followed by the bare fallow (about 90%) with the least percent aggregate stability found in plots planted with groundnuts. Similar trend was observed with the OC content at the end of the experiment while Fe/Al ratio showed a reversal, with GN, which had the lowest AS% and OC, suggesting that GN must have provide an environment that encouraged higher concentration of Fe but lower concentration of Al. his observation agrees with the report of Jonsson and Abubakar (1996), that fallow play important roles in soil fertility and crop yield, also different land management type resulted in varying inputs in the total OM content of the soil, however according to Lugo et al (1981) and Houghton et al 1991) the rate and duration of the increase will depend on the method of conversion, intensity of the subsequent land use as well as the climatic, physical and chemical

8 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.160 property of the soil under study. Generally, in this study, higher contents of Fe/Al ratio suggest soil acidity and this corresponds with the acidity level as indicated by the observed ph values ranging from 3.9 to 4.4 for all the cover management practices studied. Penetrometer resistance is an index of soil surface structure, the penetrability of a soil to any probing instrument is a rheological property which depends on the texture, structure, mineralogical composition, moisture content and compactness of the soil, thus in this study with no significant differences in BD and moisture content it is expected that the penetration resistance, would depend more on the mineralogical compositions of different plots which can be influenced by the management practice, thus in this study, the soils resistance to penetration was significantly(p= 0.05) influenced by management practice, the manure and cover management practice reduced penetration resistance relative to the bare fallow (Table 3), this also agrees with the report of kuldip et al., (1996). The management practices significantly increased the number of water drops and the energy required to breakdown soil aggregates to pass through a 4.75mm sieve. The highest drop number and energy values were obtained for aggregates formed under Panicum cover whereas the lowest values were obtained for aggregates of the bare soil. This resistance to breakdown impact could be attributed directly to the effect of Panicum maximuim on soil organic matter fraction resulting in soil aggregate formation and stabilization or indirectly to the cementation of clay particles by iron and aluminium oxides as indicated by a positive and significant correlation (r =0.819) between water drop impact and iron content in this study. Earlier reports of Mbagwu and Bazzoffi (1998) also suggest that for an aggregate to be destroyed, the detaching force of raindrop must overcome the intrinsic resisting force of soil aggregate, which depends on the cohesive forces holding the structural units together of which organic matter, iron and aluminum play important role. The management practices also influenced total porosity and macro porosity of the soil, the manure groundnut plot had the highest values for total porosity and macro porosity while he lowest values were obtained in the cassava plots. There were however no significant differences in soil bulk density under the different management practices and this could be attributed to the organic matter contents of these plots which were generally very low, this observation agree with the findings of Thomas et. al, (1996) that indicated that the amount of organic matter in any soil significantly affects its bulk density. There were significant differences in saturated hydraulic conductivity (Ksat) for the different management practices (Table3), Higher Ksat in the GN+PM, PMC and

9 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.161 GN plots is an indication of the ameliorative effect of these practices on soil structure as indicated by improvements in total porosity and Ksat in this study. This observation is confirmed by a significant and positive correlation(r= , P= 0.01) obtained between total porosity and Ksat. (Table 4). This agrees with the findings of Obi and Ofoduro (1999). Table 4: Correlation coefficients of selected parameters Parameter r-value TP vs. Ksat * TP vs. sand ** Ksat vs. sand ** BD vs. penetrometer resistance ns Water drop impact vs. Total iron ** ** Significant at p= 0.01 ns =non significant Conclusion Conclusively, the management practices significantly influenced the water properties of the soil under study. For instance, the highest drop number and energy values were obtained for aggregates formed under Panicum cover whereas the lowest values were obtained for aggregates of the bare soil, the overall trend in changes in soil water properties (Ksat, PT, and macro-porosity) was BF CS<GN<PMC<GN+PM. Also, the percent aggregate stability > 0.5 was not statistically significant but was highest for the Panicum maximum treatment closely followed by the bare fallow treatment and GN+PM treatment indicating the cover management practice can induce variation in the soil structural status were other controlling variables remain constant. Reference Adekalu, K. O. and Osunbitan J. A. (2001). Compactibility of some agricultural Soils in South Western Nigeria. Soil and Tillage Res. Vol. 59: Adeoye, K. B. (1982). Effect of tillage depth on physical properties of a tropical soil and on yield of maize sorghum and cotton. Soil Tillage Research, 2; Akamigbo, F. O.R. and Igwe, C. A. (1990). Morphology, geography, genesis and taxonomy of three soil series in eastern Nigeria. Samaru, J, Agric. Res.7: AOAC (Association of official analytical chemist) (1970). In: IITA Analytical handbook IITA, Ibadan, Nigeria. Bouyoucos, G. J. (1951). A recalibration of hydrometer for making mechanical analysis. Soil Agronomy Journal 4:

10 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.162 Houghton, R.A. Skole and Lelkowiz, (1991). Changes in Land use of Latin America between 1850 and Ecoli. Mgt 38: Jackson, M. L. (1958). Soil Chemical analysis. Prentice-Hall, Englewood Cliffs, N. J. 498pp. Jonsson, K. and Abubakar, P. (1996). Tree Fallow, a comparison between five tropical Trees SPPS Biology and Fertility of Soil 23: Klute, A (1965). Laboratory measurement of hydraulic conductivity of saturated soils. In: C. A. Black D. D Evans, J. L. White, L E. Esminger and F. E. Clark (eds.) Methods of soil analysis, Part 1 Amer. Soc of agronomy. Madison, W. I. 9: Kuldip, K., Gajri, P. R. and Arora, V. K. (1996). Estimating penetration resistance from soil physical properties. Journal of Indian Society of Soil Science 44: Little T. M. and Hills, F. J. (1972). Statistical Methods ofor Agricultural Research, First Edition. Agricultural Extension Unversity of California, Berkrley 94720, U.S.A. 242pp Lugo, Lopez, M. A., Wolf, J. M. and Perez Escolar, R. (1981). Water loss, intake, movement retention and availability in major soils of Puerto Rico. University of Puerto Rico Bulletin 264. pp 7-8. Mbagwu, J. S. C. (1989). Effect of organic amendments on some physical properties of a tropical ultisol. Biological Wastes 28: Mbagwu,J. S. C. and Bazzoffi, P. (1998). Soil characteristics related to resistanec of breakdown of dry soil aggregates by water drops. Soil and Tillage Res. 45: Mbagwu, J. S. C. and Ekwealor, G, C, (1990). Agronomic potential of brewer s spent grain. Biological Wastes, 34: Nwadialo, B. E. (1989). Soil landscape relationship in Udi-Nsukka Plateau, Nigeria. Catena 16: Obi, M. E. (1982). Runoff and soil loss from an oxisol in southeastern Nigeria under various management practices. Agric. Water Management 5: Obi, M. E. and Nnabude, P. C. (1988). The effects of different management practices on physical properties of a sandy loam soil in Southeasthern Nigeria. Soil and Tillage Res.12 : Obi, M. E. and Ofoduru, C. O. (1997). The effect of soil amendment on the physical properties of a severely degraded sandy loam soil in South Easern Nigeria. In Proc. 24 th Annual Conf. of Soil Science society of Nigeria The national. conference on soil management for food security. Usman Danfodo University, Sokoto Nigeria. pp Papendick, R. I. and Campbell, G. S. (1981). Theory and measurement of water

11 PAT 2012; 8 (1): : ISSN: ; Enyioko et al,: Soil Water Characteristics.163 potential. In: J. F. Parr, W.R, Gardner, and L. F. Elliot (eds0 Water Potential Relations in soil Microbiology, Special publication no. 9 Soil Science Soc amer, Madison Wiscoson pp1-22. Richards, L. A. (1957). Soil Moisture. USDA Year book Separate Richards, L. A. and Wadleigh, C. H. (1952). Physical changes in soils. In: Soil Physical conditions and plant growth (B. T. Shaw ed). Academic Press. N. Y Steel, R. G. D. and Torrie, J. H. (1980). Principles and procedures of statistics: A Biometric Approach (2 nd Ed.), New York McGraw-Hill Book Co. Inc. XXI : 633pp. Thomas, G. W., Haszler, G. R. and Blevins, R. L. (1996). The effects of organic matter and tillage of maximum compatibility of soil using the protector test. Soil Science 161: Tollner, E. W. Hargrove, W. L. and Laongdale, G. (1984). Influence of conventional and no-till practices on soil physical properties in the southern Piedmont. Journal of Soil and water conservation. 39: Vogel, A. I. (1961). Determination of Al using Erio-Chrome Black T as an indicator (Back titration) In: Quantitative analysis (3 rd ed.) Eng. Lang Book Soc., and Longman. Pp 436. Wood, J. C. Wood, M. K. and Tromble, J. M. (1987). Important factors influencing water infiltration and sediment production on arid lands in New Mexico Journal of Arid environment. 12: Yoder, R. E. (1936). A direct method of aggregate analysis of soils and a study of the physical nature of erosion losses. J. Am. Soc. Agron. 28: 337.